Structure: Exterior Walls | GreenBuildingAdvisor.com Feb 22, 2016 . UPDATED on February 22, 2016 Walls Must Be Durable, Well-Insulated, and Weather-Resistant. . Most structural insulated panels (SIPs) consist of an inner core of insulating foam sandwiched between outer layers of oriented strand board. SIPs take the place of conventional wood framing and, like ICFs,..